The present invention relates to an optical recording medium utilizing photochromic dye for the optical recording and/or reproduction of information.
As one of the rewritable optical recording media, there is known an optical recording medium utilizing photochromic dye. This known optical recording medium comprises a transparent substrate in the form of, for example, a disc having one surface coated with photochromic dye. When recording information, a laser beam of wavelength .lambda.1 is, while the tracking is effected, irradiated onto the recording medium, then rotated in one direction, so that the information can be stored on a spiral track as a series of spots at which photochromic reaction takes place to transform a colorless state to a colored state having an absorption band centered in the visible wavelength .lambda.2. The information readout from the optical recording medium is carried out by irradiating the recording medium with a less intense laser beam of wavelength .lambda.2 so as to pass through the series of the spots on the spiral track and then detecting, by the use of a photodetector system, absorption of the wavelength .lambda.2 from the change in intensity of light transmitted through the recording medium. Where the recording medium is irradiated with an intense laser beam of wavelength .lambda.2 in the same manner as in the recording process, the series of the spots storing the information can be erased with the photochromic dye consequently transforming from the colored state to the original, colorless state.
However, colored isomers of the photochromic dye are generally unstable and are susceptible to the natural bleaching from the colored state back to the colorless state even when placed in the dark, and therefore, it has long been considered difficult to realize an optical recording medium capable of retaining the stored information for a prolonged period of time.